Mercury boiler feed arrangement



Dec. 26, 1939. Q w ob 2,185,048

MERCURY BOILER FEED ARRANGEMENT Filed May 20, 1939 Inventor: Qrla L. Woci, b fiu/aycfx H i s Attorney.

Patented Dec. 26, 1939 UNITED stares r'rssr omcs New York ApplicationMay 20, 1939, Serial N0. 274,782

' 5 Claims. (01 103-111) The present invention relates to mercury boilerfeed arrangements including a pump, particular ly a low suction headpump for forcing mercury liquid into a boilei. In such arrangementspeear means have to be provided for returning mercury liquid l'eakingalong the pump shaft.

The objeet (if my invention is to provide an improved construction andarrangement of the type above specified whereby leakage of mercury alongthe pump shaft may be readily returned into the system. I

For a consideration of what I believe to be novel in my invention,attention is directed to the following description andthe claimsappendedthere'to in connection with the accompanying drawing. v 1

The single figure of the drawing illustrates an arrangement embodying myinvention.

The arrangement comprises a mercury boiler Ill for producing mercuryvapor. An elastic fluid turbine H has an inlet conduit I 2 with a valvel3- connected "to the boiler to receive mercury vapor therefrom and adischarge conduit I4 connected to a condenser I5 in which the exhaustfluid fromthe'turbine is condensed. 1 During normal operationthecondensate is discharged from thecondenser through a conduit l6 andforced into the boiler ID by means including a pump I! with a dischargeconduit l8 having a valve l9. The pump is of the impeller type andcomprises a pump casing 25 in which an impeller 21 is located andsecured to a vertical shaft 22 driven by a motor 23. The lower end ofthe casing forms an inlet and the upper portion of the casingforms asealing chamber 24. A mercury liquid seal is formed between the chamber24 and the'motor' 23 to prevent leakage of mercury liquid into the oillubricated motor bearings and also to prevent air from coming in contactwith and oxidizing the hot leakage mercury entering chamber 24 from theimpeller. This seal comprises a rotary sealing cup 25 secured to theshaft 22'and a stationary sealing vane 26 projecting into the sealingcup 25. Sealing liquid, in the present instance mercury, is fed to thesealing cup by a conduit 21 in which is located a cooler 26a and a valve26b which is opened to produce a small continuous mercury flow into thecup The channel 21 is connected to a conduit 28, one end of which isconnected to the aforementioned. condenser discharge conduit l5 througha valve'29, normally closed, and the other end of the conduit 28 isconnected to pump discharge conduit .l8 ahead of the valve l9 as regardsdirection of now oiliquid through the conduit it. The valve 23 is openedwhen the valve I9 is closed to recirculate the mercury While the pump isrunning to prevent f overheating and alsofor sealing the turbine shaftwhen it is sta tionary' besides acting as a vent for steam or air incase the impeller of the pump becomes bound with same.

The inlet of the pump I? is connected through a U-shaped sealing conduitto a sump 3| to receive liquid therefrom through an overflow 32 formedwithin the sump. The inlet of the sump is connected to the condenserdischarge conduit 65. The leg of the U-shaped sealing conduit tlliwhichis connected to the sump 3| has an enlarged portion 33.

During operation, mercury flows into the overflow 32 in the sump andthrough the U-shaped sealing conduit 33 and the inlet of the pump ll tobe forced by the pump through the conduit l3 into the boiler I0. Thus,normally, the condenser l5 forms the source of supply for mercury. Whenthe plant is put out of operation the mercury liquid is drained into astorage tank 34 which in the present instance is located ata level belowthe condenser and boiler. The tank 36 is connected tothe system by meansof twosurge tanks 35 and 35 having upper portions connected by apressure equalizing conduit 31 and by a conduit 38 to the condenser l5,normally to maintain vacuum in the tanks 35, 35. The surge tanks areconnected to the storage tank 34 by a conduit 39 which has a lowerportion projecting into a downward extension 40 of the bottom of thestorage tank 34, thus forming a liquid seal. The upper end of theconduit to has branches M, 42 projecting into the surge tanks 35 and 36respectively and forming over-- flows therein. The bottom portions ofthe tanks 35 and 35 are connected by a branched conduit 43 to theenlarged portion 33 of the sealing con- 'duit 30. An upper portion ofthe tank 34 is connected by a conduit M having a valve 45 to a source ofgas, preferably inert gas, under pressure. In order to force'mercuryfrom the storage tank 34 into the system the valve 45 is opened wherebymercury liquid from the storage tank 34 is forced through the conduit 39into the surge tanks 35, 35 whence it flows through the conduit 43 andthe sealing conduit 30 to the pump inlet.

I During operation some of the mercury liquid in the pump leaks into thesealing chamber 24. From this chamber the liquid is returned into the,system by means including a U-shaped s l which has one leg connected tothe chamber and another leg connected to the aforementioned U- shapedseal 30, preferably to the enlarged portion 33 thereof, that is, to theleg of the seal 30 which is connected to the sump 3|. More specificallythis U-shaped sealing conduit for returning leakage from the pump intothe system comprises a leg 46 connected bya conduit 41 to the chamber 24and a leg 48 connecting the lower end of the leg 46 to the enlargedconduit portion or chamber 33 at a point somewhat below the level of thecenter of the impeller 2| of the pump. The leg 46 has an upperopen endextending beyond the connection with the conduit 41 and enclosed in achamber 49. The chamber 49 has an upper portion connected to a conduit50 with a valve 5! for receiving gas, preferably inert gas of atmoshericpressure or pressure slightly above atmosphere. The bottom of thechamber 49 is connected to the conduit 39 by a conduit 52 forming aU-shaped seal at the lower end and including a valve 53.

Except when mercury is forced from the storage tank 34 to the surgetanks 35, 36, the valve 53 is normally open. The pressure difference inthe outlet end of the conduit 52 which is normally under vacuum as it isin communication with the condenser l5 and the chamber 49 which is underpressure preferably slightly above atmosphere is maintained by themercury seal in the U-shaped portion of the conduit 52. The differencein level of the liquid contained in the chamber 33 and in the leg 46 issubstantially equal to the vacuum maintained in the condenser [5, itbeing assumed that the condenser I5 is under vacuum and the pump I! outof operation. Upon operation of the pump the level in the chamber 33drops to a point near the connection with the leg 48 and near thehorizontal plane through the center of the impeller by the amount ofdifferential pressure between the designed suction or inlet head on thepump for the then existing discharge, and the amount of vacuummaintained in condenser I5. In any case, even with maximum vacuum incondenser 15, provided the pump is in normal operation and dischargingthe same amount of liquid in the discharge conduit 18 that is enteringit through the conduit l6 and the U-shaped sealing conduit 30, the levelin the chamber 33 will never reach such a height that the level in theleg 46 will approach the entrance of the conduit 41. The level in thechamber 33 is indicated by a stand pipe 54 connected to the U- shapedsealing conduit 30 and including a float 55. If the level rises to acertain point above the horizontal center line through the impeller, anupper portion of the float 55 actuates an alarm switch 56. Such rise ofthe mercury level may be caused, for example, if the pump I! is renderedinoperative and it also takes place during starting when mercury liquidis forced from the storage tank to the pump. Likewise there is a similaralarm switch 59 which the float 55 actuates if the pump attempts to pumpitself dry with a consequent drop in level by the valves l9 being leftopen or too far open for the amount of return entering the pump fromcondenser l5. During starting the level indicator notifies the operatorwhen to start the pump and also when to admit inert gas, such asnitrogen, by opening the valve 5| to the sealing chamber 24. The rotarymercury seal 25, 26 prevents leakage of gas into the atmosphereand'leakage of air into the sealing chamber. This is best accomplishedby a gas pressure in the sealing chamber slightly above atmosphere. Theavoidance of air leakage into the sealing chamber is important inmercury boilers because of the oxidation of mercury that would otherwiseresult. In case of an emergency shut-down of the pump with fullvacuum'in the condenser, the mercury liquid in the chamber 33 will riseabove its connection with the conduit 43 and the mercury liquid will beforced into the surge tanks 35, 36, the latter as stated before beingunder vacuum. As the level in the surge tanks rises to the height of theoverflow pipes 4|, 42 the liquid will be returned through theseoverflows into the storage tank 34. During shut-down the vacuum in thecondenser is ordinarily broken by the admission of inert gas such asnitrogen. The mercury liquid then draining into the chamber 33 of thesealing leg 30 causes considerable rise in level in the sealing leg 46.As the mercury level in this leg rises to the open upper end of the leg46 above the connection with the conduit 41, the mercury liquid flowsinto the chamber 49, whence it is drained through the sealing conduit 52to the storage tank 34. The upper end of leg 46 is located at a levelnear that of the rotary mercury seal 25, 26. The cross-section of thechamber 49 is large relative to that of the area of the open end of theleg 46. This enables the chamber to take large overfiow without muchincrease in head, thus preventing the mercury level in the pump sealingchamber 24 to rise above the sealing cup 25. I

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Mercury boiler feed arrangement comprising a source of mercury, afeed pump, means including a U-shaped sealing conduit connecting theinlet of the pump to the dischargeof the'condenser, and means includinga U-shaped sealing pipe for returning leakage from the pump into saidsealing conduit.

2. Mercury boiler feed arrangement compris+ ing a source of mercury, afeed" pump having a casing with a portion forming an inlet and anotherportion forming a sealing chamber, means including a liquid sealconnecting the inlet to the condenser, and means forming another. liquidseal connecting the sealing chamber to the first liquid seal. 1

3. Mercury boiler feed arrangement compris- I ing a, condenser, a feedpump forming a sealing chamber, means forming a liquid seal connectingthe inlet of the pump to the discharge of the condenser, means fordraining leakage from the chamber to the liquid seal comprising aU-shaped sealing device having one leg connected to said liquid seal,and means connecting the other leg to the chamber and to a source ofinert gas under pressure.

4. Mercury boiler feed arrangement comprising a source of mercuryliquid,.a vertical pump having a shaft with an impeller, an inlet belowthe impeller and a sealing chamber above the impeller, means including aU-shaped sealing conduit having a first leg connected to the inlet and asecond leg connected to the source, and means including a .U-shapedsealing pipe having a first leg connected to the sealing chamber and asecond leg connected to the second leg of said conduit to return leakagefrom the chamber 'to the sealing conduit, and means forming an overflowfor the first leg of the sealing pipe and having a liquid seal toreceive mercury as the mercury level in the sealing chamber rises beyonda certain height.

ORLA L. WOOD.

